Hey there, let's dig into why your Android project suddenly started throwing this AAPT error out of nowhere—even without any intentional updates. Based on your description and the build.gradle code you shared, here are the most likely fixes to try:

1. Fix Mismatched Support Library Versions #

Looking at your dependencies, there's a big red flag: you're using a wildcard (+) for the RecyclerView library:

compile 'com.android.support:recyclerview-v7:+'

This tells Gradle to auto-pull the latest RecyclerView version, which might be higher than your compileSdkVersion 26 and other support libraries (like appcompat-v7:26.0.1 or design:26.0.1). Mismatched support library versions are a top cause of AAPT resource processing failures.

Quick Fix: Replace the wildcard with a fixed version that matches your other support libraries:

compile 'com.android.support:recyclerview-v7:26.0.1'

2. Align Compile SDK & Build Tools Versions #

You mentioned upgrading your SDK to 27.0.0, but your build.gradle still uses compileSdkVersion 26 and buildToolsVersion "26.0.1". Mismatches between your installed SDK and the versions specified in your build script often trigger AAPT errors.

Option A (Stick to SDK 26):
Double-check that you still have the SDK 26 platform and build tools 26.0.1 installed in the SDK Manager. If you deleted them when upgrading to 27, reinstall them.

Option B (Upgrade to SDK 27):
Update your build.gradle to match the SDK 27 version you installed. Here's how to adjust it:

android {
    compileSdkVersion 27
    buildToolsVersion "27.0.3" // Use the latest stable build tools for SDK 27

    defaultConfig {
        // Keep other settings the same
        targetSdkVersion 27
    }
    // Rest of your android block stays unchanged
}

dependencies {
    // Update all support libraries to match SDK 27 (27.1.1 is the latest stable)
    compile 'com.android.support:appcompat-v7:27.1.1'
    compile 'com.android.support:recyclerview-v7:27.1.1'
    compile 'com.android.support:design:27.1.1'
    // Keep other dependencies as-is
}

3. Check for Invalid or Corrupted Resource Files #

AAPT errors often hide in your app's resources (XML layouts, drawables, strings) even if you didn't modify them. Common issues include:

• Syntax errors in XML files (unclosed tags, typos in attribute names)
• Duplicate resource IDs across different files
• Resource filenames with special characters (spaces, Chinese characters, symbols)
• Corrupted drawable files (try re-adding any custom images you're using)

Fix: Scan your res/ directory—Android Studio usually highlights XML errors with red underlines, so start there.

4. Additional Troubleshooting Steps #

If the above fixes don't work, try these:

• Restart Android Studio: Sometimes IDE cache glitches cause weird issues that a simple restart can fix.
• Disable AAPT2 (temporarily): Add android.enableAapt2=false to your gradle.properties file. The new AAPT2 resource processor can sometimes have compatibility issues with older projects.
• Clean & Rebuild via Terminal: Run ./gradlew clean build from the terminal (instead of IDE buttons) to ensure a full, thorough clean.

Let me know if any of these steps get your project running again!

内容的提问来源于stack exchange，提问作者Uday